1. Field of the Invention
The present invention relates to a method for setting up a traffic channel connection between mobile stations of a mobile radiotelephone network with radio base stations, a radio base station control unit that controls the radio base station, and a mobile switching center physically connected with this control unit via a transcoding and rate adaption unit. In addition, the invention relates to arrangements for implementing such a method.
2. Description of the Prior Art
Mobile radiotelephone networks, are generally specified according to the ETSI recommendation GSM. "GSM" is currently used as an abbreviation for the English expression "Global System for Mobile Communications", and there are three basic classifications: the GSM900 class, wherein the radio system operates with a carrier frequency in the 900 MHZ range, the DCS1800 class, wherein the radio system operates with a carrier frequency in the 1.8 GHz range, and the PCS 1900 system, operating with a carrier frequency of 1.9 GHz.
The GSM network is hierarchically organized into several subsystems, namely a radio subsystem RSS, a network switching subsystem NSS and an operation and maintenance subsystem OMS.
The radio subsystem RSS contains the mobile telephones, which are also called mobile stations MS and which respectively communicate via radio with the nearest base station, also called the base transceiver station BTS. The base stations are part of the base station subsystem, within which they can maintain traffic channel connections and signaling channel connections via so-called Abis interfaces to base station control units BSC, and can be controlled by these base station control units. The base station control units can be connected with the network switching subsystem via transcoding and rate adaption units TRAU through traffic channels and signaling channels, in particular with mobile switching centers of the network switching subsystem, which are also designated mobile switching center MSC. The interface between the base station subsystem BSS and the network switching subsystem NSS is designated A-interface. Besides at least one mobile switching center, the network switching subsystem NSS also contains a database system, in order to be able to execute the switching and management tasks that arise. Important registers of this database system include, for example, the home location register HLR, in which personal subscriber information, such as e.g. telephone number, services cleared for the subscriber, home location to which the subscriber is allocated and his current location, are stored. Moreover, there is a visitor location register VLR that contains the dynamic subscriber data. This register comes to contain local databases allocated to the area. Copies of the home location registers for those users currently located in the coverage area of such a visitor register VLR are maintained in these databases. In addition, the database system of the network switching subsystem contains an authentication center AUC that contains the access data of the individual subscribers, in particular the secret SIM card key personally allocated to a subscriber, which is required for the access of the subscriber to the mobile radiotelephone network, as well as for the coded transmission of the speech data via the network. In addition, there is an apparatus database with terminal-apparatus-specific data, also designated equipment identity register EIR.
When a subscriber sends a connection request from a mobile station registered in a mobile radiotelephone network in the manner described above to another mobile station of this mobile radiotelephone network, this connection request is signaled by means of a signal transmission via the base station BTS in whose radio area he is located, via the base station control unit BSC that controls this base station BTS, and via the transcoding and rate adaption unit TRAU allocated to this base station control unit BSC, to a mobile switching center MSC allocated to this transcoding and rate adaption unit. Using a database--here using the home location register HLR--the mobile switching center determines which of the base stations can be used to reach the mobile station to which a connection request was signaled. After an authentication process between the mobile switching center and the destination mobile station, the mobile switching center of the network switching subsystem produces a switching through of the traffic channel connection between the two mobile stations. This traffic channel connection is routed, by the originating mobile station emitting the connection request, via the base station nearest this originating mobile station, via the base station control unit allocated to this base station, via a transcoding and rate adaption unit, via a switching stage in the mobile switching center, via a transcoding and rate adaption unit, via a base station control unit and via a base station located nearest the destination mobile station. Traffic channel connections for a very large area with a very large number of mobile stations are always switched via a single mobile switching center.
Since a large portion of connections between mobile stations of a mobile radiotelephone network are required within a spatially limited region, and each traffic channel connection requires a channel bandwidth from an element of the base station subsystem to the mobile switching center, and likewise requires such a bandwidth from the mobile switching center to this element of the base station subsystem, the transmission line network between these base station subsystem elements and the mobile switching center is heavily loaded.